This invention relates to a fuel injection system for an engine and more particularly to an improved fuel injection system and method of injecting fuel into an internal combustion engine to promote stability in running under all conditions.
The advantages of direct cylinder injection for internal combustion engines are well known. By employing direct cylinder injection, it is possible to provide some stratification of the fuel charge, particularly at low and mid range performance, which stratification can significantly improve not only fuel economy but control of exhaust gas emissions, particularly unburned hydrocarbons. However, the amount of fuel injected at idle and low speed is extremely small. If the engine is spark ignited, it must be insured that a stoichiometric mixture is present at the gap of the spark plug at the time of firing.
It has also been realized that the stability of an engine can be significantly improved by having so called "fast burn" of the charge. The advantages of fast burn are particularly prevalent at idle and low speeds when a small fuel charge is present in the chamber. Fast burn can be promoted by incorporating a device for increasing the turbulence in the combustion chamber. One way which turbulence is normally generated is through the use of a squish area that cooperates with a recess or pocket type combustion chamber with the squish charge being transferred at a rapid velocity into the combustion chamber adjacent the time of ignition. However, where the squish action is employed, there is some risk that the fuel charge may be swept away from the spark plug and in stability can result.
It is, therefore, a principal object to this invention to provide a improved arrangement for injecting fuel directly into the combustion chamber of an engine and still maintaining good running and stability under idle and low speed operation.
It is a further object to this invention to provide an arrangement for injecting fuel into an internal combustion engine in such a way so as insure stability even at low and mid range speeds so as to achieve good performance and exhaust emission control.
One form of fuel injection employs not only the injection of fuel under pressure but also the injection of air under pressure. The pressurized air is injected along with the fuel and the air pressure assists in dispersion and vaporization of the fuel particles. However, where air is employed to assist in the fuel injection, the problems associated with stratification and insuring a proper stoichiometric fuel/air mixture in the vicinity of the spark plug at the time of firing are greatly magnified.
It is, therefore, a still further object to this invention to provide an improved air/fuel injection system and method of operating such a system that will provide good stability under all running conditions and particularly under low speed, low load conditions.